The invention relates to optical switches and in particular to an optical switch including a movable waveguide that is selectively evanescently coupled to a fixed waveguide by moving a micromechanical cantilever structure.
In multi-channel communication systems, it is desirable to provide a selective coupling mechanism. This allows signal channels to be added to lines and dropped from lines or switched from line to line. It may also be desirable to provide for the splitting of a signal channel among multiple lines. To realize a large communications network, it may be desirable to provide arrays of such switches and signal splitters and numerous separate communications lines for the various channels. Desirably these arrays may be packaged together as an integrated multiplexer/demultiplexer device, which is compact, has low loss characteristics, and creates little cross talk between channels.
Additionally, a multi-channel communication network desirably contains a plurality of controllable switching means to allow rerouting of data signals within the network. This allows the flow of signal channels to be interactively altered during operation.
It may be desirable for the functions of the switches and signal splitters to be combined with controllable switching functions. This situation may be accomplished through the use of controllable switches. An array of such controllable switches may be seen as a simple, rapid reconfigurable integrated multiplexer/demultiplexer device. Such a device may allow the data flow patterns within a communications network to be almost instantaneously rerouted.
Fiber optics communication systems provide a method of streamlining the communications lines. A single optical fiber can carry a large number of separate communication channels, each channel operating bidirectionally at a different wavelength. The larger the number of wavelengths that may operate simultaneously within a fiber, the greater the capacity of the fiber.
Several factors determine what the maximum number of wavelengths operating in a single fiber can be. The first factor is the spectral range over which the fiber has a low enough loss and a high enough confinement factor to make transmission practical. The second factor is the spectral width of the laser sources used for the communications system and how much these spectra are broadened during transmission through the system. A third factor is the precision with which the channels may be separated from one another.
Providing a compact, highly discriminating, low loss multiplexing system for multi-wavelength optical communication systems has been very challenging. Some approaches that have been tried include; dynamically configurable gratings, prisms, or filters. While these means are perfectly adequate for many multiplexing systems, they suffer the drawback that the number of channels that the system may handle is limited because the wavelength dispersion of the demultiplexing means is not adequate to separate very closely spaced channels in devices of reasonable dimensions. Additionally, these approaches are not easily amenable to miniaturization.
Other wavelength multiplexers have been described in the literature. For example, frequency selective coupling means, i.e., evanescent couplers, have been proposed as an alternative to means that rely on dispersive properties of the multiplexer components. An evanescent coupler, in its simplest embodiment, uses at least two optical waveguides in such close proximity that the propagating mode of the second waveguide is within the exponentially decaying evanescent portion of the propagating mode of the first waveguide. The overlap couples optical energy into the second waveguide if the propagation constants, k, in the two guides are equal. If the values of k are equal at only a single frequency, only energy at that frequency is coupled while energy at other frequencies remains in the first guide. H. F. Taylor describes such a frequency selective coupling scheme in Optics Communications, 8, pp. 421-425, August 1973. The couplers described used optical coupling between two non-identical waveguides to couple the single optical frequency for which the propagation constants in the two guides are equal. The systems described in this text, however, are not readily controllable.
The present invention is embodied in a micromechanical optical switch structure that may be integrated to form an array of optical switches. The switch switches light between a main waveguide and a switched waveguide. The switched waveguide has a coupling portion and two flexible portions and is coupled to a movable cantilever arm. The cantilever arm is configured to move at least the coupling portion of the switched waveguide between at least first and second positions with respect to the main waveguide. In the first position, the switched waveguide is evanescently coupled to the main waveguide and in the second position, the switched waveguide is not evanescently coupled to the main waveguide.